The present invention relates to a method for detecting decompression of tires and a device thereof, and a program for judging decompression of tires. More specifically, the present invention relates to a method for detecting decompression of tires which can broaden a region of judging decompression of tires and improve the accuracy of reduced pressure judgment and a device thereof, and a program for judging decompression of tires.
A conventional device for detecting decompression of tires uses a principle that since the outer diameter of a tire (the effective rolling radius of a tire) is reduced more than that of a tire having a prescribed inner pressure (normal air pressure) when the pressure of a tire is reduced, wheel speed (rotational angular velocity) is increased as compared with other normal tires. For example, a method of detecting the lowering of an inner pressure from the relative difference of the wheel speed of a tire uses as a judgment value;DEL={(V1+V4)/2−(V2+V3)/2}/{(V1+V2+V3+V4)/4}×100(%)(For example, Japanese Unexamined Patent Publication No. 305011/1988).
Wherein V1 to V4 are the wheel speeds of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
Further, as an alternative device for detecting decompression of tires, there is a device judging decompression of tires by comparing the wheel speeds of respective tires with the speed against ground of a vehicle which can be measured by GPS (Global Positioning System) and time (Japanese Unexamined Patent Publication No. 146037/2003).
However, since the above-mentioned method compares the wheel speeds on a pair of diagonals relatively, it cannot judge the simultaneous decompression of two front wheel tires or the simultaneous decompression of two rear wheel tires, and further the simultaneous decompression of whole wheel tires. Accordingly, there are problems that continuous drive without knowing decompression causes the deterioration of mileage caused by the increase of rolling resistance of tires, and further causes burst of a tire.
Further, drive wheels generate slip in accordance with drive. More driving force on the road surface of a slope with gradient than on a flat road is specifically required, and slip quantity is increased in proportional to the driving force. Since slip in drive wheels is generated on a steep slope and the like, reduced pressure judgment cannot be accurately carried out, and it is occasionally judged to be reduced pressure nevertheless the tire is prescribed inner pressure. Further, when a vehicle runs on the road surface of a slope, load distribution to front and rear tires is changed, and when the load of wheels is enlarged, the effective rolling radii of tires are lessened, therefore it is occasionally judged to be reduced pressure nevertheless the tires are the prescribed inner pressure.
Further, since the effective rolling radii of tires are changed by centrifugal force, lateral acceleration and the like other than the gradient of a slope as factors affecting a vehicle, it is occasionally judged to be reduced pressure nevertheless the tires are the prescribed inner pressure.
Accordingly, it is difficult to improve the accuracy of reduced pressure judgment only by comparison of the wheel speeds of respective tires and only by comparison of the wheel speeds with the speed against ground of a vehicle.